The present invention relates to magnet wires having good self-lubricating properties.
Recently, manufacturers of electric apparatuses that use magnet wires have come to use high-speed automatic winding machines to increase the speed of the production line. The increased line speed at first seemed to cut the production cost by a substantial degree. However, it has now been found that the gains in production were more than offset by costs incurred as a result of damage caused to the wire and coating by friction and other mechanical stress during the high speed winding. If such damaged wire is assembled in an electric machine, layer shorting (short-circuiting between wires) occurs and the loss factor is increased to an undesirably high level.
To minimize the mechanical damage to the enamel coating, magnet wires having good self-lubricating properties have been demanded. Self-lubricating are necessary not only for use with an automatic winder but also because magnet wires are often inserted manually into a small slot in a motor. Since magnet wires themselves do not have good self-lubricating properties, the low slip factor between individual wires, between wires and the winder and between wires and the electrical machine into which they are assembled causes mechanical damage to the enamel coating or decreases the efficiency of the winding and assembling operations.
This problem has partly been solved by coating the magnet wire with a layer of various liquid lubricants such as liquid paraffin and refrigerator oil. But the resulting wires still do not have satisfactory lubricating and slip properties and cannot be handled efficiently in manual operation. Furthermore, such wires cannot be wound into a neat coil for making, e.g., a transformer, as the speed of the automatic winder has been increased further and the use of an inserter to achieve a higher space factor is more common these days.
Insufficient bonding of the magnet wires has become another factor which increases the chance of layer shorting. Improving the self-lubricating properties of magnet wires by applying a large quantity of liquid lubricants is not very effective. On the contrary, when this is done more dirt collects on the magnet wires and the bonding strength of adhesive tape used to fix the end of the coil is adversely affected. Attempts have been made to eliminate these defects by coating the magnet wires with solid lubricants such as solid paraffin and carnauba wax having better lubricating properties than liquid lubricants. To form a uniform coating on the magnet wires, the solid lubricants are usually applied to the wires from a solution having a few percent of the lubricant dissolved in solvents such as petroleum benzine, toluene and xylene. However, the use of a large quantity of low-boiling solvent is not only hazardous to human health but it also produces electric wires with creasing or crazing that do not have much commercial value. Therefore, coating with solid lubricants can only be applied to limited types of electric wires. Furthermore, if magnet wires coated with these solid lubricants are applied to motors that are to be immersed in refrigerants, the lubricant coating is extracted by the refrigerant and can clog the opening of the compressor valve or the refrigerant expansion nozzles in the refrigerator. This will reduce the refrigerating capacity of the machine. In addition, if the lubricant is extracted by the refrigerant, the self-lubricating properties of the magnet wire are reduced and the enamel coating becomes vulnerable to mechanical damage due to electromagnetic vibration.
Another method that has been proposed for providing magnet wires with high lubricating properties is to use enamel compositions containing synthetic resins having good lubricating properties such as polyethylene, polypropylene and polytetrafluoroethylene, as well as silicone oil, fluorine containing surfactants, and liquid and solid lubricants such as paraffin wax, carnauba wax and montan wax. However, synthetic resins such as polyethylene, polypropylene and polytetrafluoroethylene are sparingly soluble in solvents for the enamel and are difficult to disperse in the enamel uniformly, and the resulting enamel is not highly stable. What is more, these resins are not highly miscible with the insulating components of the enamel so they are difficult to disperse in the enamel coating uniformly and the resultant enamel coating does not have a good appearance. Liquid lubricants in the enamel provide an enamel coating whose slip and self-lubricating properties are as low as those of the coating formed by applying them onto the magnet wire. Solid lubricants in the enamel are sometimes extracted by refrigerants or solvents after the enamel is applied to the electric wire (the same thing happens when solid lubricants are directly applied to the magnet wire), and the magnet wire produced in this manner is not readily usable with motors that are to be immersed in refrigerants. Furthermore, like synthetic resins, the solid lubricants are sparingly soluble in solvents for making an enamel and they are not highly miscible with the insulating components of the enamel. Therefore, the resultant enamel is not stable and the lubricants are difficult to disperse in the enamel coating uniformly. Therefore, coatings produced in this manner do not have a good appearance.